Okay, here's a report on the Odyssey grille block (and bug deflector delete). The van warms up quickly, but water temp locks in solid at 181 F around town and in steady highway driving. Over some 2600 miles of highway driving from Washington to Colorado and back for Christmas vacation, the highest temp I ever saw momentarily was 189. Interestingly, it's not a long hill climb; but the downhill coast afterwards with an idling engine when the temp needle climbs, I assume due to slower water pump speeds.
There were too many variables and poor previous data collection to put a good number on the improvement (I'm also driving faster since confirming that the Ody's speedo reads 4 mph slow at highway speeds (but not the ODO!). However, over this trip during 70-75 mph daytime driving, the van got 21-23 mpg, and the best tank was 25.8 mpg at 65 mph at night (with a tank of 85 octane Idaho ethanol winter blend). This was over some steep highways; we saw 6% for over 6 miles on two occasions, with many other dramatic climbs not posted.